Monitoring Vaccines for Safety

The National Network for Immunization Information describes how vaccines are monitored in the United States:

The safety of vaccines is continuously monitored and studied by programs such as:

  • Vaccine Adverse Events Reporting System

  • Vaccine Safety Datalink Project

  • National Vaccine Injury Compensation Program

  • Task Force on Safer Childhood Vaccines

  • Institute of Medicine research studies

Vaccine Adverse Events Reporting System

Sometimes a person will develop adverse signs or symptoms after receiving a vaccine. Healthcare providers are required to report certain adverse health effects that occur after a child is vaccinated. For example, if a child is hospitalized or dies after receiving a vaccine, this adverse event must be reported. The adverse event may have been caused by something other than the vaccine, such as an infection, a pre-existing illness, or an injury, but there is a small chance that the event was caused by a vaccine. The monitoring systems allow scientists to gather enough data to determine which events may be related to vaccines.

In 1990, the FDA and the CDC established the Vaccine Adverse Events Reporting System (VAERS) so that reports could be collected and analyzed. As many as 12,000 reports have been made in a single year, and about 2,000 of these reported serious illness or death. All reports are entered into a database; the FDA and the CDC use the data to monitor vaccine safety and conduct research studies. However, with further examination, most of these events have been found to be unrelated to vaccines. VAERS reports do not establish cause and effect. Only large epidemiologic studies can show that the vaccine caused the adverse event.

To ensure that all relevant data are captured, the VAERS allows anyone to file a report if they suspect that their child or patient has a vaccine-related reaction. Because entries are not screened, the database contains events that are related and unrelated to vaccines. The FDA monitors the VAERS to determine whether any vaccine is associated with more adverse events than would be expected due to chance.

Recently, the rotavirus vaccine was withdrawn from the market after VAERS reports identified 15 cases of severe bowel obstruction in infants who received it. The VAERS data were used as a "signal" that the vaccine might be causing the problem; however subsequent epidemiological studies were necessary to establish that the vaccine was likely responsible.

To date, a definite causal relationship has not been established.

VAERS Contact Information
Phone: 1-800-822-7967

Vaccine Safety Datalink Project

Unlike the VAERS database, large linked databases allow research scientists to have access to the complete medical records of millions of people who receive vaccines. (Patient identity is not released).

In 1990, the CDC developed the Vaccine Safety Datalink Project to study rare side effects from vaccines. Four large health maintenance organizations provide the CDC with medical information on more than 6 million people. The large number of patients makes this project a powerful tool for examining the relationship between a specific vaccine and serious side effects.

Since its initiation in 1990, the Vaccine Safety Datalink Project has conducted surveillance on about 500,000 children from birth through age 6 years (2 percent of the U.S. population in this age group). These data were used to study the rate of Sudden Infant Death Syndrome (SIDS) after anecdotal evidence suggested a possible link to the DTP vaccine. The risk of SIDS was found to be the same for vaccinated children as for unvaccinated children enrolled in the participating health maintenance organizations. Such studies are known as "post-marketing" or "Phase IV" clinical studies because the vaccine has been approved by the FDA for marketing.

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Important disclaimer: The information on is for educational purposes only and should not be considered to be medical advice. It is not meant to replace the advice of the physician who cares for your child. All medical advice and information should be considered to be incomplete without a physical exam, which is not possible without a visit to your doctor.

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